Background: Problematic stimulant (i.e., crystal methamphetamine [meth], cocaine, crack) use is a prevalent and treatment refractory problem in men who have sex with men (MSM), and highly predictive of both condomless sex and HIV infection. This application builds off of our successful formative and pilot work and is designed to assess the efficacy, in a three-arm randomized controlled trial (RCT), of Project IMPACT?a behavioral intervention to reduce high-risk sex in MSM with stimulant use disorder who are at risk for HIV acquisition. The intervention incorporates risk reduction counseling with behavioral activation (BA) to help participants re-engage in enjoyable and meaningful life activities not involving drugs. Behavioral activation is an evidence-based, easy to administer, cognitive behavioral approach to treat depression and other problems that focuses on helping individuals reengage in activities that generate feelings of enjoyment (i.e., mastery and pleasure). We chose this strategy for MSM with stimulant use disorder because our formative work revealed that MSM who abuse stimulants report becoming unable to enjoy activities that they previously enjoyed as a result of ongoing stimulant use. This lack of enjoyment (i.e., anhedonia, one of the core symptoms of depression) in activities that do not involve stimulant use or sex contributes to the continued use of stimulants and potentially unsafe sex. We developed and openly field-tested this intervention in a NIDA-funded non- randomized pilot (R03 DA023393), and, subsequently, conducted a NIDA-funded pilot RCT (R34 DA031028) of this intervention compared to a standard of care condition (SOC) and found it to be feasible, acceptable, and successful at reducing both condomless anal sex and stimulant use. The proposed efficacy trial is the next logical step in this program of research. Conceptual Model: The conceptual model focuses on anhedonia?a loss of interest in previously enjoyed activities?as a consequence of continued stimulant use. Accordingly, for individuals with stimulant use disorder, drug use becomes the central means for obtaining enjoyment, and hence BA will augment HIV risk reduction counseling. Research Plan Overview: 286 MSM who are at risk for HIV infection and meet DSM-5 diagnostic criteria for stimulant (amphetamine) use disorder will be recruited from two study sites [(1) New England: Boston/Providence and (2) Miami] with excellent access to this population. Two-fifths of the sample (n = 114) will be randomized to the IMPACT intervention; two-fifths (n = 114) to an active, credible time-matched control (relaxation and educational support), and one-fifth (n = 58) to a standard-of- care (SOC) control. Participants will be followed for 12 months. Main outcomes include number of condomless anal sex acts without protection of PrEP (primary) and the number of stimulant use episodes (secondary). We will also collect resource utilization and cost data to examine the cost-effectiveness of the intervention.